Spatial sound systems providing an enhanced spatial experience over traditional stereo or mono systems have become very popular. For example, surround systems with five or seven spatial channels (often in addition to one or two Low Frequency Effect (LFE) channels) have become very popular for applications such as Home Cinema systems.
In many situations it is desirable to have small form factor loudspeakers. However, the small size invariably affects the amplitude and low frequency response of the sound reproduction. As such there is typically a trade-off between the audio quality and the physical form factor for the loudspeakers. In addition, spatial sound systems often exacerbate the issues as they not only tend to use a larger number of loudspeakers but also restrict the degree of freedom in the placement of these as the sound source position is of importance for the spatial perception.
For example, surround sound systems such as Home Cinema systems make use of multiple loudspeakers to create an immersive sound experience similar to that of a full size cinema. For the most convincing and immersive sound experience all the loudspeakers must be capable of full range audio reproduction. Furthermore, the loudspeakers must be positioned at appropriate positions to provide the desired spatial experience. This requires large loudspeakers which are often unsightly and difficult to position in a room. Many consumers find the additional loudspeakers provide too much clutter. It is therefore desirable to reduce the size of some or all of the loudspeakers such that they are less visible and can be more easily incorporated into a room. In particular, the rear loudspeakers are often considered to be inconvenient in terms of size and positions. However, as the dimensions of the loudspeakers are reduced, so too is the low-frequency performance and the maximum Sound Pressure Level (SPL) achievable at a given frequency.
To address such issues most home cinema systems employ a satellite subwoofer arrangement, where the satellites are approximately full range sound reproducers, and the subwoofer reinforces only the lowest frequencies. Satellite subwoofer arrangements typically require the crossover frequency from subwoofer to satellite loudspeakers to be as low as possible. In a room environment localization of low-frequency (<120 Hz) sound sources is difficult. This enables almost free placement of the subwoofer within the room. If the crossover frequency is too high (above 120 Hz), the localization cues relating to the subwoofer become apparent making the low-frequency source easy to locate. For good sound quality and proper stereophonic imaging effects, the satellites must therefore be capable of almost full range sound reproduction. If the satellites are not capable of covering the full audio range from 120 Hz to 20 kHz the system is compromised. The designer can chose either to leave a gap in the frequency response of the system from 120 Hz to the low-frequency cut off of the satellite loudspeakers, or increase the crossover frequency to the subwoofer. Both of these compromises reduce the audio quality and immersive listening experience.
Thus, in many scenarios trade-offs between size and positioning of loudspeakers on one hand and audio quality and spatial experience on the other hand tend to be suboptimal.
Hence, an improved sound reproduction system would be advantageous and in particular a system allowing for increased flexibility, increased freedom in positioning loudspeakers, improved audio quality, increased sound pressure levels, an improved spatial experience and/or improved performance would be advantageous.